From: Nikolai Lugovoi on
Here is another oddity, and I could not trace source of it:

irb(main):001:0> Gem::ConfigMap
=> {:EXEEXT=>"", :RUBY_SO_NAME=>"ruby", :arch=>"i686-linux",
:bindir=>"/home/nlugovoi/lib/ruby/bin",
:libdir=>"/home/nlugovoi/lib/ruby/lib", :ruby_install_name=>"ruby",
:ruby_version=>"1.9.1",
:rubylibprefix=>"/home/nlugovoi/lib/ruby/lib/ruby",
:sitedir=>"/home/nlugovoi/lib/ruby/lib/ruby/site_ruby",
:sitelibdir=>"/home/nlugovoi/lib/ruby/lib/ruby/site_ruby/1.9.1"}
irb(main):002:0> Gem.path
=> ["/home/nlugovoi/.gem/ruby/1.9.1",
"/home/nlugovoi/lib/ruby/lib/ruby/gems/1.9.1"]
irb(main):003:0> Gem.clear_paths
=> nil
irb(main):004:0> Gem::ConfigMap
=> {:EXEEXT=>"", :RUBY_SO_NAME=>"ruby", :arch=>"i686-linux",
:bindir=>"/home/nlugovoi/bin", :libdir=>"/home/nlugovoi/lib",
:ruby_install_name=>"ruby", :ruby_version=>"1.9.1",
:rubylibprefix=>"/home/nlugovoi/lib/ruby",
:sitedir=>"/home/nlugovoi/lib/ruby/site_ruby",
:sitelibdir=>"/home/nlugovoi/lib/ruby/site_ruby/1.9.1",
:datadir=>"/home/nlugovoi/share",
:vendordir=>"/home/nlugovoi/lib/ruby/vendor_ruby",
:vendorlibdir=>"/home/nlugovoi/lib/ruby/vendor_ruby/1.9.1"}
irb(main):005:0> Gem.path
=> ["/home/nlugovoi/.gem/ruby/1.9.1", "/home/nlugovoi/lib/ruby/gems/1.9.1"]

so, at the moment of loading, Gem::ConfigMap points to wrong
directories, :rubylibprefix=>"$HOME/lib/ruby/lib/ruby" instead of
:rubylibprefix=>"$HOME/lib/ruby", and fixes that only after
Gem.clear_paths

How can that happen that in gem_prelude.rb ConfigMap receives such
incorrect values?

From: Nikolai Lugovoi on
Actually, that seems to be a bug, introduced in svn rev26881, that results in :

ruby.c:448:
rb_const_set(rb_cObject, rb_intern_const("TMP_RUBY_PREFIX"),
rb_obj_freeze(rb_str_new(RUBY_LIB_PREFIX,
sizeof(RUBY_LIB_PREFIX)-1)));

added to ruby bugs: http://redmine.ruby-lang.org/issues/show/2978

sorry for the noise